Maximum binding of proteinA-fusion protein to IgG agarose

Dear researchers,
Does anyone know the condition for maximum binding of proteinA-fusion
protein to IgG agarose? When I used a spent medium of transfected cells as
a source for the purification, I failed to purify it. Does it need to
adjust pH to the optimal condition for binding to IgG agarose?
Welcome any comments and suggestions.
Jun-ichi Aikawa, Ph.D.
University of California, San Diego